Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85902
Applications&Innovations deterioration increased each year and is likely due to snowplow effects. The flow characteristics have been measured each year, with high infiltration results and good consistency from year to year. Operations during rain events indicate that the pervious overlay quickly removes rainwater from the pavement surface and that the water migrates lateral to the side of the pavement, in- dicating pervious concrete is a successful tool for mitigat- ing splash and spray as well as reducing hydroplaning difficulties. Wet-on-dry overlays are the standard for traditional concrete overlays, says Kevern, Ph.D., LEEP AP, who developed an effective wet-on-dry mix design for pervious concrete overlays. "Pervious is normally pretty dry. There is not a lot of ex- tra paste so it took a bit of research to produce good bonding characteristics." In terms of performance, "the pervious concrete overlay mix isn't being designed to be structural pavement, but we're developing a mix strong enough to have good bonding characteristics." Testing confirmed that curing under plastic was a viable technique. The top picture shows plastic secured to keep the wind out. The final surface texture was uniform and durable. This was the first time it had been tried for a pervious con- crete overlay, he says, and it also was the first wet-on-dry per- vious concrete overlay in the United States. Previously, it had been tested in Belgium, The Netherlands, Japan and Australia. "This placement is wet-on-dry, which is much more difficult than wet-on-wet. Wet-on-wet has been constructed in various locations and we know it works but, is complicated and expen- sive to construct. Wet-on-dry would be much cheaper but, until now no one has successfully built one." The project was designed to place the overlay with a slip- form paver, but because of scheduling, it was placed using semi-mechanized placement. The next step is to fully mecha- nize placement of the pervious concrete overlay as slipform. "The next phase is to get it on an open facility with high- speed traffic," Kevern says, although the test track undergoes the rigors of a fair amount of traffic and plowing, which is a good durability test, "We ultimately need to get it in service in a small installation before this moves to widespread use." If the use of these kinds of pervious concrete overlays moves to widespread use, they may have a bright future in noise reduction, particularly in urban areas. "This has half the noise generation of normal concrete," Kevern points out. "This is where the overlay would shine – in urban areas – where there are noise considerations." However, pervious is a fil- ter, so an area where there is a heavy amount of dirt being tracked on and off the pavement would not be an appropriate application site for this type of overlay. Better Roads January 2012 31